Present day kinematics of Italy

Abstract

We present the velocity field of Italy derived from the analysis of continuous GPS observations collected during 1998-2009 from 287 sites. The GPS networks analyzed cover the whole country with a mean inter-site distance of about 50 km. The processing is performed using two software programs, BERNESE and GAMIT, adopting in both cases a distributed session approach with more than 10 clusters, sharing common stations, each of them consisting of about 40 stations. Daily loosely constrained solutions (saved as SINEX files) are routinely produced for each cluster by two data analysis centres and the velocity field is obtained by stacking the daily normal equations. The rigorous combination of independent solutions allows the cross-validation of the velocity field. We have analyzed the time series of the entire area referenced to a common frame (ITRF2005 with respect to Eurasian Plate) and have estimated the velocity field providing an updated detailed picture of the kinematics (velocity map) and deformation pattern (strain rate map) of the Italian area. Additionally, we have combined the two velocity fields obtained from the two software programs obtaining the average velocity field of the Italian area. The two velocity fields agree at the level of 0.2-0.3 mm/yr consistent with their standard deviations. The deformation patterns (strain-rates) do have significant features, showing a distinctive extension along the Apennines on the order of 50-80 10-9 yr-1 and less pronounced areas of compressive tectonic behaviour at the level of 30-50 10-9 yr-1. The GPS kinematic description of the crustal deformation shows a high coherence with the seismotectonic setting of the Italian area.